It is proposed to complete the development to a practical stage of application of a newly devised electromagnetic method for simultaneous measurement of average and phasic volume rate of blood flow, blood velocity and vascular diameters. The new method utilizes a magnet external to the animal's body so that its magnetic field traverses the blood vessels under study inducing an e.m.f. in the blood stream which constitutes the flow signal. The induced flow signal is picked up by means of an ultra-miniature intravascular probe which is inserted into the vessels under study much as a guide wire via an angiographic catheter (the probe is a loop made of an insulated spring wire 0.1 mn in diameter). The loop probe can be inserted into small branches of the aorta via angiographic catheter of standard size (#7 French) an will easily pass even through much smaller catheters (down to #4 French). The same transducer can be utilized to detect even minute variations in phasic and average artery diameter. It is proposed to develop such transducers to a high degree of perfection and to sizes permitting measurements in arteries and veins down to 1 mm in diameter and to develop appropriate methods of "delivery" i.e., of conveying the sensing element to the appropriate blood vessel, assuring optimal position and orientation of the sensor relative to the external magnetic field. The proposed research will involve exploration of all of the important blood vessels supplying the vital organs (such as renal, mesenteric, internal carotid and coronary arteries) and development of the simplest possible techniques of recording such regional blood flows in anesthetized animals. Such methodological work will involve improvement of the design of the flow and diameter sensors as well as of the electronic channels for amplification of the electrical flow signals and for current supply to the magnet. After completion of this phase of the project, possibilities will be explored and developed to eliminate the external magnet and to obtain on the basis of the same electromagnetic induction principle and with the same sensor tracings of blood flow and vascular diameter changes in conscious moving subjects and the beating heart.